In railroads, the standard rail fastener, nearly from the beginning, has been the spike, driven into a wood tie on each side of the rail base to maintain gage. Tie plates have been employed which act as bearing pads against vertical forces and maintain the desired rail cant. Laterally spaced stops in the plate parallel to the rail line maintain gage. The tie plate is apertured to receive one or more spikes. Longitudinal restraint is provided by anticreeper devices attached to the bottom of the rail base on both sides of the tie. This time-honored arrangement is called a floating rail seat because there is no attempt to directly fix the rail to the tie; consequently, there is limited restriction to rail uplift or tipping. This is used for most rail installations today, but there are special cases as exceptions. One case is that of the concrete tie where spiking cannot be used and electrical insulation is needed because, unlike wood, the tie is not an insulator; therefore, conventional steel tie plates and anticreeper devices cannot be used. Another case occurs with severe railroad curves where the lateral thrust of the car wheels may be of such magnitude there is a possibility of the rail tipping to such an extent that derailment may occur.
Direct fixation fasteners have been used to prevent rail uplift and tipping. The earliest of these fasteners were stiff bolts tightened down on the rail base. These were prone to failure by pulling out of the tie or by fatigue because of their high stiffness. Resilient fasteners were introduced which had low stiffness so they could move with the rail but still maintain direct fixation. Direct fixation fasteners provide for longitudinal and lateral restraint replacing or augmenting spikes and anticreeper devices. In concrete tie applications, non-metallic tie pads and insulators isolate the rail electrically.
Certain terms of art have been used in describing resilient fasteners. The clip is a spring which applies a hold-down force (toe load) to the rail base; the shoulder is a rigid chair or anchor member embedded in the cross tie, providing a rigid mount for the clip. All such devices heretofore constructed react the toe load by socketing action, producing an upward load on the shoulder (shoulder load) and a downward load (heel load) on a part of the shoulder termed the shelf. The arm of the clip which contacts the rail is thus cantilevered from the shoulder. In the present design, the toe load is produced by wedging one arm of the clip between the rail and shoulder rather than by cantilevering, therefore, no heel load is present.